The present invention relates, in general, to the method of brazing and coating of metallic alloy members and, more particularly, to a method of brazing beryllium-aluminum alloy members to form a beryllium-aluminum alloy assembly and coating the beryllium-alloy assembly.
Beryllium-aluminum alloy members have tenacious oxide surfaces making it difficult to join or coat.
Heretofore, beryllium-aluminum alloy members were joined mechanically, by adhesive bonding, by dip brazing, and by vacuum furnace brazing. The mechanical bonding of beryllium-aluminum assemblies by nuts and bolts added significant weight and space to the assemblies. The adhesive bonding of beryllium-aluminum alloy members did not provide adequate strength and was not a totally satisfactory medium for transferring thermal energy. Dip brazing of beryllium-aluminum alloy members required the beryllium-aluminum alloy members to be precisely machined to form small joint gaps in order to keep the brazing alloy in the joints during the heating process. It was found that dip brazing to form a moderate to complex assembly provided inadequate braze fillets, if any. Braze fillets are desirable in beryllium-aluminum alloy assemblies, since joint stresses are carried by fillets rather than by faying surfaces. In the vacuum furnace brazing of a beryllium-aluminum alloy members, the faying surfaces of the beryllium-aluminum alloy members required thorough cleaning by grinding and by the use of chemicals. Such pre-cleaning processes were followed by applying a direct pressure on the joint during brazing.
Oxide surfaces naturally form on beryllium-aluminum alloy members. With oxide surfaces on the beryllium-aluminum alloy assembly, an anodic coating could not be readily formed on the beryllium-aluminum alloy assembly of sufficient thickness or of sufficient hardness to provide a wear resistant coating or an electrical insulating coating of the quality formed on aluminum. Beryllium-aluminum alloy assemblies were coated with primers, paints and by plating.
An object of the present invention is to provide an improved method for brazing beryllium-aluminum alloy members to form a beryllium-aluminum alloy assembly.
Another object of the present invention is to provide a method for coating beryllium-aluminum alloy members to achieve greater hardness for the coating and to achieve improved abrasive resistant and electrical insulating characteristics for the coating.
Another object of the present invention is to provide a method for coating a beryllium-aluminum alloy assembly by removing oxidized surfaces from the beryllium-aluminum alloy assembly and thereafter coating the surfaces of the beryllium-aluminum alloy members free of oxides to achieve improved wear resistance and to achieve improved abrasive resistant and electrical insulating characteristics for the coating.
Another object of the present invention is to provide a method for brazing beryllium-aluminum alloy members to form a beryllium-aluminum alloy assembly without significantly increasing weight and without significantly increasing the space occupied by the beryllium-aluminum alloy assembly.
Another object of the present invention is to provide a method for brazing beryllium-aluminum alloy members for improving the transfer of thermal heat energy in a beryllium-aluminum alloy assembly.
Another object of the present invention is to provide a method for brazing beryllium-aluminum alloy assemblies without the need for applying direct pressure to the joint during the brazing process.
Another object of the present invention is to provide a method for brazing beryllium-aluminum alloy members to facilitate the maintaining of a braze alloy in the joints of a beryllium-aluminum alloy assembly during the heating process.
Another object of the present invention is to provide a method for brazing beryllium-aluminum alloy members by forming braze fillets in the joints of a beryllium-aluminum alloy assembly which fill the gaps in the joints of the beryllium-aluminum alloy assembly and which are suitable for carrying stress loads in the joints of the beryllium-aluminum alloy assembly.
Briefly described, the method of the present invention for brazing beryllium-aluminum alloy members to form a beryllium-aluminum alloy assembly comprises the following steps:
(a) cleaning the surface of beryllium-aluminum alloy members;
(b) placing beryllium-aluminum alloy members to form a beryllium-aluminum alloy assembly;
(c) disposing a braze alloy at locations to form braze joints;
(d) applying a brazing flux to the braze alloy at the braze joint locations, the brazing flux comprising the following;
potassium chloride
aluminum fluoride
sodium chloride
sodium fluoride
lithium fluoride; and
(e) heating the beryllium-aluminum alloy members and the braze alloy to form the beryllium-aluminum alloy assembly.
Briefly described, the method of the present invention for coating a beryllium-aluminum alloy assembly after brazing the beryllium-aluminum alloy members comprises the steps of:
(a) cleaning the surfaces of the beryllium-aluminum alloy members; and
(b) coating the surfaces of the beryllium-aluminum alloy members by plasma deposition of alumina-titania.